The present invention relates to a heat treatment method and a heat treatment apparatus.
Heat treatment apparatuses are used in fabricating semiconductor devices to heat-treat workpieces, such as semiconductor wafers, for oxidation, diffusion, CVD, annealing and the like. A known vertical heat treatment apparatus is provided with a heat treatment furnace capable of heat-treating a plurality of semiconductor wafers in an atmosphere of a predetermined process gas. This known heat treatment apparatus has a casing serving as an outer covering, and a vertical heat treatment furnace provided with an opening in a lower portion thereof and disposed in a back upper region in the casing. A loading area extends under the heat treatment furnace.
Arranged in the loading area are a transfer mechanism for transferring semiconductor wafers between a carrier, i.e., a carrying container capable of containing a plurality of semiconductor wafers, and a wafer boat, i.e., a holder for holding semiconductor wafers, and a lid lifting mechanism for vertically moving a lid for covering the opening of the heat treatment furnace, loaded with the wafer boat mounted on a heat insulating cylinder placed on the lid to carry the wafer boat through the opening into and to carry the same out of the heat treatment furnace. The casing is provided in its back part with an entrance to enable an operator to enter the loading area for maintenance and a door to close the entrance.
The heat treatment apparatus is controlled during a general process so that pressure in the loading area of the heat treatment apparatus is slightly higher than pressure in the environment surrounding the heat treatment apparatus by 3 to 5 Pa to prevent the leakage of the ambient atmosphere into the loading area.
When the heat;treatment apparatus is used for a process that uses a dangerous gas, such as arsine (AsH3), as a process gas, there is a danger of unstable substances, such as the dangerous gas and particles, remaining on semiconductor wafers held on the wafer boat leaking from the loading area outside the heat treatment apparatus even if the atmosphere in the heat treatment furnace is replaced with an inert gas, such as nitrogen gas (N2). Therefore it is difficult to carry out a process that uses a dangerous gas by the heat treatment apparatus.
The present invention has been made in view of the foregoing circumstances and it is therefore an object of the present invention to provide a heat treatment method and a heat treatment apparatus capable of preventing the leakage of a specific gas and particles outside from a loading area thereof and of safely carrying out a process that uses a dangerous gas. Another object of the present invention is to provide a heat treatment apparatus capable of selectively carrying out a low-negative-pressure operation or a low-positive-pressure operation.
According to a first aspect of the present invention, a heat treatment method includes the steps of: transferring workpieces from a clean room outside a loading area to the loading area; carrying the workpieces from the loading area into a heat treatment furnace to subject the workpieces subjected to a predetermined heat treatment process; and returning the heat-treated workpieces from the heat treatment furnace to the loading area; wherein the loading area is evacuated to have a predetermined negative pressure relative to the clean room at least when returning the workpieces to the loading area.
The heat treatment method in the first aspect of the present invention may evacuate the loading area to the predetermined negative pressure relative to the clean room when carrying the workpieces from the loading area into the heat treatment furnace.
The heat treatment method in the first aspect of the present invention may evacuate the loading area to a low negative pressure in the range of xe2x88x921 to xe2x88x923 Pa relative to the clean room.
The heat treatment method according to the first aspect of the present invention may give an alarm when pressure in the loading area is in the range of xe2x88x920.5 to xe2x88x921 Pa relative to the clean room during the evacuation of the loading area.
The heat treatment method in the first aspect of the present invention may remove a specific gas and particles discharged from the loading area by filters during the evacuation of the loading area.
According to a second aspect of the present invention, a heat treatment apparatus includes: a loading area for storing workpieces transferred thereto from a clean room; a heat treatment furnace connected to the loading area to process workpieces transferred from transferred the loading area for performing a predetermined heat treatment process; an exhaust for evacuating the loading area; and a controller for controlling the exhaust so that the loading area is evacuated to have a predetermined negative pressure relative to the clean room.
In the heat treatment apparatus in the second aspect of the present invention, the exhaust may be provided with filters for removing a specific gas and particles discharged from the loading area.
In the heat treatment apparatus in the second aspect of the present invention, the filters may include an ULPA filter and a chemical filter.
The heat treatment apparatus in the second aspect of the present invention may further include a differential pressure gauge for measuring pressure difference between the loading area and the clean room, the differential pressure gauge being connected to the controller.
In the heat treatment apparatus in the second aspect of the present invention, the controller controls the pressure in the loading area at a low negative pressure in the range of xe2x88x921 to xe2x88x923 Pa relative to the clean room.
In the heat treatment apparatus in the second aspect of the present invention,
an alarm device may be provided for giving an alarm when the pressure in the loading area is in the range of xe2x88x920.5 to xe2x88x921 Pa relative to the clean room.
According to a third aspect of the present invention, a heat treatment apparatus includes: a loading area for storing workpieces from a clean room; a heat treatment furnace connected to the loading area to process workpieces transferred from the loading area for performing a predetermined heat treatment process; an exhaust for evacuating the loading area; a gas supplier for supplying a gas into the loading area; and a controller for controlling the exhaust and the gas supplier.
The heat treatment apparatus according to the third aspect of the present invention may further include a selector means for selectively changing an operating mode of the controller between a low-negative-pressure operating mode in which at least the exhaust is controlled so that the loading area is set at a predetermined negative pressure relative to the clean room and a low-positive-pressure operating mode in which at least the gas supplier is controlled so that the loading area is set at a predetermined positive pressure relative to the clean room.
In the heat treatment apparatus according to the third aspect of the present invention, the exhaust may be provided with filters for removing a specific gas and particles received from the loading area.
In the heat treatment apparatus according to the third aspect of the present invention, the filters may include an ULPA filter and a chemical filter.
The heat treatment apparatus according to the third aspect of the present invention may further include a differential pressure gauge for measuring pressure difference between the loading area and the clean room, the differential pressure gauge being connected to the controller.
In the heat treatment apparatus according to the third aspect of the present invention, the controller may control the pressure in the loading area at a negative pressure in the range of xe2x88x921 to xe2x88x923 Pa relative to the clean room.
In the heat treatment apparatus according to the third aspect of the present invention, an alarm device may be provided for giving an alarm when the pressure in the loading area is in the range of xe2x88x920.5 to xe2x88x921 Pa relative to the clean room.